This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We have proposed to develop a novel MRI reporter gene system that uses MRI to monitor gene expression and the status of cell grafts in vivo. Current MRI technology is capable of high spatial resolution at 10-mm range and has found wide applications in research as well as in the clinical diagnosis of various diseases. In vivo monitoring of cell grafts is a critical function for the future development of cell replacement based therapy. Although applications of MRI in cell tracking and monitoring have shown great promise, technical challenges have also been recognized. As cell grafts are not expected to differ in water content from surrounding tissues, they alone do not generate signals detected by MRI. MagA regulates the transport of iron and the formation of magnetite (Fe3O4) crystals in certain types of bacteria. Magnetite is a supermagnetic particle that can induce the substantial changes in water relaxation times and is therefore considered an excellent MRI contrast agent. Our lab has successfully expressed MagA in mammalian cell lines and confirmed the formation of magnetosomes, which can be readily detected in MRI. We hypothesize that MagA could be expressed in mouse embryonic stem cells (mESCs) without an adverse effect on the stem cell properties that allow an mESC graft to be monitored noninvasively by MRI. We propose to evaluate the potential of MagA as an MRI reporter gene for cell graft monitoring in vivo, one of the major barriers in advancing cell replacement research.